John Gallagher Montgomery (June 27, 1805 – April 24, 1857) was a lawyer who represented Pennsylvania in the U.S. Congress briefly in 1857.
Montgomery was elected as a Democrat to the Thirty-fifth Congress and served until his death.
He attended the inauguration dinner for President Buchanan at the National Hotel where he was reported to have been deliberately poisoned, along with many other attendees.
This incident is now known as National Hotel Disease, and is believed to have been caused by food poisoning related to poor sanitation.
Montgomery returned home ill, and died at Danville five weeks later.